1. Field of the Invention
The invention relates generally to power supplies and more specifically to active circuits used as filters for controlling conducted radiation, such as the coupling of noise generated by switching power supplies back into their sources of power.
2. Description of the Prior Art
A common technique for distributing electrical power around a vehicle, vessel and even a building involves stringing an unregulated power supply bus around to all the points that will consume power and then to place a voltage regulator at each of the points of consumption. Each individual voltage regulator can then supply an appropriate voltage to its respective load.
Switching power supplies have become popular because they offer high efficiency and can produce voltages above or opposite to the incoming power source voltage. However, switching power supplies can generate noise that is both radiated and directly coupled to its inputs and outputs. With higher power levels, the generated noise can be very energetic and difficult to control. The radiated noise can typically be controlled with proper shielding and the conducted noise is conventionally filtered out. Without adequate filtering, an unregulated common power source can couple noise between equipment loads and cause erratic operation. Highly sophisticated gear tends to be the most susceptible, in particular to their highly sensitive radio receivers, such as used in navigation instrumentation.
Capacitors and inductors, and even capacitor and resistor combinations have long been used in pi-network and T-network configurations to construct filters. However, capacitors and inductors large enough to control noise in distributed-point regulation configurations can be bulky and expensive.
Conventional filters have been designed to filter out AC to DC rectification chop to provide a smoothed voltage to a load downstream of the power supply. An unusual situation is encountered in distributed-point regulation configurations because the smoothing is required upstream of the load, in particular, upstream of the switching power supply and its associated load. This requirement is opposite to what has been the conventional circuit design problem.